BY C. HEDLEY. 291 



Vertagus bituberculatus Sowerby, Conch. Icon., xv., 1865, PI. iv., 

 fig. 7; Id., Thes. Conch, iii., C'erithium suppl., 1866, PI. 290, fig. 

 324. 



Cerithium cordigerum Bayle (nom. mut.), Journ. de Conch., 

 xxviii., 1880, p. 249. 



In the British Museum there are two specimens, apparently types 

 of bituberculatus, which drew my attention to this novel synonymy. 

 Had Bayle examined the subject carefully, he would have found 

 that the renomination of Lamarck's species had already been effec- 

 tively, if unconsciously, accomplished. 



The habitat has not hitherto been announced more definitely than 

 "New Holland" or "Australia." Specimens sent to me by Mr. F. 

 H. Moore show it to be plentiful at the entrance of the Irwin River, 

 West Australia. 



Plesiotrochus unicinctus A. Adams. 

 (Plate xviii., fig. 63.) 



Ziziphinus unicinctus A. Adams, Proc. Zool. Soc, 1851 (1853), 

 p. 167. 



Four specimens in the British Museum are evidently, though not 

 so marked, the types of this species, described as "On pearl oysters, 

 8 to 10 fathoms, Lord Hood's Island," or Marutea, Paumotus. It 

 has never been figured, redescribed, or properly classified. Study 

 of these types enables me to pronounce Z. unicinctus an absolute 

 synonym of Trochus exilis Pease, from the same place, and of 

 Plesiotrochus souverbianus Fischer from the Loyalty Islands. 

 Hence it will stand as the type of the genus. To support this con- 

 clusion I now offer a figure of one of the original specimens of 

 Adams. 



In these Proceedings (antea xxxii., p. 498), I lately reviewed the 

 genus Plesiotrochus, since when it has been reported from the 

 Indian Ocean by Mr. E. A. Smith in the person of Plesiotrochus 

 fischeri* 



* Smith, Proc. Malac. Soc, viii., 1909, p. 370, text-fig. 



